Linda A. Hunt

Observations of infrared radiative cooling in the thermosphere on daily to multiyear timescales from the TIMED/SABER instrument

16 17 Abstract. We present observations of the infrared radiative cooling by carbon dioxide (CO2) and 18 nitric oxide (NO) in Earths thermosphere. These data have been taken over a period of 7 years 19 by the SABER instrument on the NASA TIMED satellite and are the dominant radiative cooling 20 mechanisms for the thermosphere. From the SABER observations we derive vertical profiles of 21 radiative cooling rates (W m -3 ), radiative fluxes (W m -2 ), and radiated power (W). In the period 22 from January 2002 through January 2009 we observe a large decrease in the cooling rates, 23 fluxes, and power consistent with the declining phase of solar cycle 23. The power radiated by 24 NO during 2008 when the Sun exhibited few sunspots was nearly one order of magnitude 25 smaller than the peak power observed shortly after the mission began. Substantial short-term 26 variability in the infrared emissions is also observed throughout the entire mission duration. 27 Radiative cooling rates and radiative fluxes from NO exhibit fundamentally different latitude 28 dependence than do those from CO2, with the NO fluxes and cooling rates being largest at high 29 latitudes and polar regions. The cooling rates are shown to be derived relatively independent of 30 the collisional and radiative processes that drive the departure from local thermodynamic 31 equilibrium (LTE) in the CO2 15 μm and the NO 5.3 μm vibration-rotation bands. The observed 32

Short-term periodic features observed in the infrared cooling of the thermosphere and in solar and geomagnetic indexes from 2002 to 2009

We report derivations of short-term periodic features observed in time series of the radiative cooling of the Earth’s thermosphere. In particular, we diagnose observations of the infrared emission from nitric oxide (NO) at 5.3 μm to reveal periodicities equal to the solar rotation period (27 days) and its next three harmonics. From 2002 to 2009 we observe 27 day, 13.5 day, 9 day and (occasionally) 6.75 day periods in the thermospheric NO cooling, the solar wind speed and the Kp geomagnetic index. Periodic features shorter than 27 days are absent in the time series of the 10.7 cm radio flux (F10.7) over this same time period. The periodic features in the NO cooling are found to occur throughout the depth of the thermosphere and are strongest at high latitudes. These results confirm the persistent coupling between the solar corona, the solar wind and the energy budget of the thermosphere.

Influence of solar variability on the infrared radiative cooling of the thermosphere from 2002 to 2014

Infrared radiative cooling of the thermosphere by carbon dioxide (CO2, 15 µm) and by nitric oxide (NO, 5.3 µm) has been observed for 12 years by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics satellite. For the first time we present a record of the two most important thermospheric infrared cooling agents over a complete solar cycle. SABER has documented dramatic variability in the radiative cooling on time scales ranging from days to the 11 year solar cycle. Deep minima in global mean vertical profiles of radiative cooling are observed in 2008–2009. Current solar maximum conditions, evidenced in the rates of radiative cooling, are substantially weaker than prior maximum conditions in 2002–2003. The observed changes in thermospheric cooling correlate well with changes in solar ultraviolet irradiance and geomagnetic activity during the prior maximum conditions. NO and CO2 combine to emit 7 × 1018 more Joules annually at solar maximum than at solar minimum. Key Points First record of thermospheric IR cooling rates over a complete solar cycle IR cooling in current solar maximum conditions much weaker than prior maximum Variability in thermospheric IR cooling observed on scale of days to 11 years

Impact of equinoctial high‐speed stream structures on thermospheric responses

We examine thermospheric neutral density response to 172 solar wind high-speed streams (HSSs) and the associated stream interfaces during the equinox seasons of 2002–2008. HSSs produce prolonged enhancements in satellite drag. We find responses to two drivers: (1) the equinoctial Russell-McPherron effect, which allows the azimuthal component of the interplanetary magnetic field (IMF) to project onto Earths vertical dipole component, and (2) coronal streamer structures, which are extensions of the Suns mesoscale magnetic field into space. Events for which the IMF projection is antiparallel to the dipole field are classified as “Effective-E;” otherwise, they are “Ineffective-I.” Effective orientations enhance energy deposition and subsequently thermospheric density variations. The IMF polarities preceding and following stream interfaces at Earth produce events that are Effective-Effective-EE, Ineffective-Ineffective-II, Ineffective-Effective-IE, and Effective-Ineffective-EI. These categories are additionally organized according to their coronal source structure: helmet streamers (HS-EI and HS-IE) and pseudo-streamers (PS-EE and PS-II). Approximately 65% of these combinations are HS-EI or HS-IE. The response to HS-IE structures is smoothly varying and long-lived, while the response to PS-EE structures is erratic, short-lived, and modulated by thermospheric preconditioning. We find significant distinguishable responses to these drivers in four geomagnetically sensitive observations: low-energy particle precipitation, proxied Joule heating, nitric oxide flux, and neutral density. Distinct signatures exist in neutral density response that can be anticipated days in advance based on currently available knowledge of on-disk coronal holes. Further, we show that the HS-IE events produce the largest neutral density disturbances, with δρmax,IE exceeding δρmax,EI by more than 30%.

A combined solar and geomagnetic index for thermospheric climate

Infrared radiation from nitric oxide (NO) at 5.3 µm is a primary mechanism by which the thermosphere cools to space. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the NASA Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics satellite has been measuring thermospheric cooling by NO for over 13 years. In this letter we show that the SABER time series of globally integrated infrared power (watts) radiated by NO can be replicated accurately by a multiple linear regression fit using the F10.7, Ap, and Dst indices. This allows reconstruction of the NO power time series back nearly 70 years with extant databases of these indices. The relative roles of solar ultraviolet and geomagnetic processes in determining the NO cooling are derived and shown to vary significantly over the solar cycle. The NO power is a fundamental integral constraint on the thermospheric climate, and the time series presented here can be used to test upper atmosphere models over seven different solar cycles. Key Points F10.7, Ap, and Dst replicate time series of radiative cooling by nitric oxide Quantified relative roles of solar irradiance, geomagnetism in radiative cooling Establish a new index and extend record of thermospheric cooling back 70 years

Atomic hydrogen in the mesopause region derived from SABER: Algorithm theoretical basis, measurement uncertainty, and results

Atomic hydrogen (H) is a fundamental component in the photochemistry and energy balance of the terrestrial mesopause region (80–100 km). H is generated primarily by photolysis of water vapor and participates in a highly exothermic reaction with ozone. This reaction is a significant source of heat in the mesopause region and also creates highly vibrationally excited hydroxyl (OH) from which the Meinel band radiative emission features originate. Concentrations (cm−3) and volume mixing ratios of H are derived from observations of infrared emission from the OH (υ = 9 + 8, Δυ = 2) vibration-rotation bands near 2.0 µm made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. The algorithms for deriving day and night H are described herein. Day and night concentrations exhibit excellent agreement between 87 and 95 km. SABER H results also exhibit good agreement with observations from the Solar Mesosphere Explorer made nearly 30 years ago. An apparent inverse dependence on the solar cycle is observed in the SABER H concentrations, with the H increasing as solar activity decreases. This increase is shown to be primarily due to the temperature dependence of various reaction rate coefficients for H photochemistry. The SABER H data, coupled with SABER atomic oxygen, ozone, and temperature, enable tests of mesospheric photochemistry and energetics in atmospheric models, studies of formation of polar mesospheric clouds, and studies of atmospheric evolution via escape of hydrogen. These data and studies are made possible by the wide range of parameters measured simultaneously by the SABER instrument.

Intercalibration of neutral density measurements for mapping the thermosphere

This paper describes a technique for mapping exospheric temperatures, derived from neutral density measurements from the Challenging Mini-satellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) satellites. The Naval Reasearch Laboratory Mass Spectrometer, Incoherent Scatter Radar Extended Model (NRLMSISE-00) thermosphere model is used for the conversion. Adjustments for each satellite were needed in order for the time-averaged densities to agree with the model. It was necessary to correct for inexact modeling of the annual and semiannual oscillations in the density, as well as the declining densities during the solar minimum. It was found that a time-varying perturbation in the atomic oxygen in the model could produce a good agreement at both altitudes. The time series of this oxygen variation was found to have a very high correlation with independent measurements of CO2 emissions measured with the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument. The temperature data are averaged on a spherical grid having equal areas in each pixel, avoiding functional fits that would blur finer details. The use of solar magnetic rather than geographic coordinates enhances the auroral ovals. There are strong elevations in the exospheric temperatures in the polar regions, particularly near the dayside cusp. Spatial filtering with spherical wavelets is used to remove statistical fluctuations, although some details are lost. The exospheric temperature maps are well ordered by the nitric oxide emission measurements from SABER. The technique that is described here could be applied to future improvements of empirical density models, having an accuracy and spatial resolution that is not presently available.

Generating 275-m Resolution Land Surface Products From the Multi-Angle Imaging SpectroRadiometer Data

This paper shows how to reconstruct the original 275-m resolution data of the Multi-angle Imaging SpectroRadiometer (MISR) instrument in the 24 spectrodirectional global mode channels that are spatially averaged to 1.1 km on-board the Terra platform, with negligible loss of information relative to images acquired in native-resolution local mode. Standard approaches to improve the spatial resolution of products rely on one (typically panchromatic) high-resolution (HR) image to sharpen multiple spectral images. In the case of the MISR-HR package described here, three of the 12 available HR channels are combined to regenerate each of the 24 reduced-resolution channel to its native resolution. The accurate and rigorously reconstructed spectral bidirectional reflectance data allow sensitive and physically meaningful land surface attributes to be recovered at a spatial resolution appropriate to document the spatial heterogeneity of the land surface and relevant for climate and environment studies. MISR has been in continuous operation since February 2000 and provides global coverage in at most nine days (depending on latitude). This technique allows the generation of quantitative information to monitor change and model ecosystem function virtually anywhere and at any time during the last decade. The potential is demonstrated for a savanna landscape in South Africa.

Localized thermosphere ionization events during the high‐speed stream interval of 29 April to 5 May 2011

We analyze localized ionospheric-thermospheric (IT) events in response to external driving by a high-speed stream (HSS) during the ascending phase of the Solar Cycle 24. The HSS event occurred from ~ 29 April to 5 May, 2011. The HSS itself (and not the associated corotating interaction region) caused a moderate geomagnetic storm with peak SYM-H = −55 nT and prolonged auroral activity. We analyze TIMED (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics)/SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) measurements of nitric oxide (NO) cooling emission during the interval as a measure of thermospheric response to auroral heating. We identify several local cooling emission (LCE) events in high to subauroral latitudes. Individual cooling emission profiles during these LCE events are enhanced at ionospheric E layer altitudes. For the first time, we present electron density profiles in the vicinity of the LCE events using collocated COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) radio occultation (RO) measurements. Measurements at local nighttime show the formation of an enhanced E layer (about 2.5 times increase over the undisturbed value) at ≥100 km altitude. Daytime electron density profiles show relatively smaller enhancements in the E layer. We suggest that the IT response is due to additional ionization caused by medium energy electron (>10 keV) precipitation into the subauroral to high-latitude atmosphere associated with geomagnetic activity during the HSS event.

Effects of two large solar energetic particle events on middle atmosphere nighttime odd hydrogen and ozone content: Aura/MLS and TIMED/SABER measurements

It is well established that large solar energetic particle (SEP) events affect ozone in the middle atmosphere through chemical reactions involving odd hydrogen (HOx) species. We analyze global middle atmospheric effects at local nighttime for two large SEP events during the intervals of 7–17 November 2004 and 20–30 August 2005. Properties of the SEP events and concomitant geomagnetic storms are discussed using in situ measurements. Temporal dynamics and latitudinal distribution of HOx and ozone densities inferred from measurements by the Aura/MLS (Microwave Limb Sounder) instrument are analyzed. We show statistically significant increases of nighttime hydroxyl (OH) density in the middle atmosphere up to 5°106 cm−3 in the latitude range from 70° down to 50° latitude in northern and to −40° latitude in southern hemispheres in connection with peaks in proton fluxes of >10 MeV energy range measured by GOES spacecraft. During the storm main phases, the nighttime OH density increases were observed around ±50° in southern and northern hemispheres in the altitude range of 65–80 km. There is a correspondence between averaged nighttime OH partial column density (in 0.005 to 0.1 hPa pressure range) in the polar latitudes and energetic proton (>10 MeV) fluxes. Corresponding statistically significant nighttime ozone destructions up to 45% are observed from 70° down to 60° latitude in the northern and southern hemispheres. The SEP impulsive phases correspond to onsets of ozone density depletions. Larger relative ozone destructions are observed in the northern hemisphere in November and in the southern hemisphere in August. Simultaneous measurements of ozone density by the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) instrument independently confirm the MLS results.